1. Field of the Invention
This invention relates to a friction plate for use in a lock-up clutch, a brake or the like used in the automatic transmission or the like of a vehicle.
2. Related Background Art
FIG. 6 of the accompanying drawings is a front view of a friction plate 21 according to the prior art on which frictional material segments are stuck. As shown in FIG. 7 of the accompanying drawings, a long frictional material sheet 22 is fed out and punched at an equal pitch to obtain a plurality of frictional material segments 23.
As shown in FIG. 7, a radius R describing an arc 26 disposed on the inner peripheral side of the core plate 28 of the frictional-material segment 23 and a radius R describing an arc 27 disposed on the outer peripheral side of the core plate 28 are equal to each other. This shape further improves the yield of the material as compared with a case where frictional material segments of a shape along the inner and outer peripheral edges of the core plate 28 are punched.
The prior art friction plate 21 is obtained by sticking the thus obtained frictional material segments 23 on the annular core plate 28. A spline 29 to be fitted to the hub of a partner member is provided on the inner periphery of the core plate 28, and oil paths 30 for discharging lubricating oil are provided at predetermined intervals among the segments.
When the frictional material segments 23 are continuously punched by a press, the frictional material segments 23 are cut twice. Particularly, a side extending in the diametral direction and an arc on the upstream side with respect to the feeding direction are cut together, while on the other hand, an arc on the downstream side with respect to the feeding direction is already cut at one pitch. With regard to the arc portion on the downstream side, the cutting clearance is great even when a minute pitch error occurs, and the stress produced during the cutting of a frictional material sheet can be relieved by flexure. However, with regard to the corner portion, when the cutting of the side extending in the diametral direction intersecting with the upstream arc is done, a localized force is applied and thus, the stress introduced cannot be sufficiently relieved by flexure alone, and cutting refuse is produced. As the result, the powder-like cutting refuse produced by the minute error of pitch feeding accumulates in and around the metal mold of the press. Further when the press continues to be operated with this cutting refuse left as it is, there arises the inconvenience that excess stress or the like is produced to thereby accelerate the wear of the punch and dies of the metal mold or cause the breakage of the dies.
The present invention has as its object to eliminate or decrease the production of the abovementioned cutting refuse to prevent the wear and damage of the metal mold of a press for punching frictional material segments.
To achieve the above object, the friction plate of the present invention is a friction plate comprising a substantially annular core plate and a frictional material segment stuck on the core plate with the center point of the core plate as the center, wherein the frictional material segment has inner and outer peripheries comprising two arcs having the same radius, a concave cut-away portion provided at at least one of corner portions joining sides of the frictional material segment to at least one of the inner and outer peripheries.
Also, the friction plate of the present invention is characterized in that the cut-way portion preferably include at least one arc.
The friction plate of the present invention is further characterized in that the radius of the arc of the cut-away portion is at least 0.2 mm.
Also, the present invention provides a punching apparatus having a punch and a die and for punching a frictional material segment from a frictional material, wherein the frictional material segment has inner and outer peripheries comprising two arcs having the same radius, and a concave cut-away portion provided at at least one of corner portions joining sides of the frictional material segment to at least one of the inner and outer peripheries.
In the friction plate of the present invention, the frictional material to be stuck on the core plate is made into segments, and is further made into a shape in which the radii of arcs disposed on the inner and outer peripheral edge sides of the frictional material segments are the same. Further, when this shape is punched into equal pitches by a press, a cut-away portion is provided at two corner portions located in a direction in which the frictional material is fed out. This cut-away portion has the same center as the center of the arc disposed on the inner peripheral side of the core plate of the frictional material segments and is larger by an amount corresponding to the depth forming the cut-away portion than the radius forming the arc of the inner peripheral side.
The corner portion constituted by the sides forming the cut-away portion is made into an arc, and the radius forming the arc is at least 0.2 mm.
Also, each of the frictional material segments includes inner and outer peripheries comprising two arcs having the same radius and a cut-away portion is provided at at least one of corner portion joining sides of the frictional material segment to at least one of the inner and outer peripheries. The punching surface and die of the punch have a corner portion at which at least one of the inner and outer peripheries and the sides linking the opposite ends of the inner and outer peripheries together intersect with each other.